Apparatus and method for controlling a greenhouse environment

ABSTRACT

A method of controlling an environment in a greenhouse, the method comprising: periodically venting air from inside to outside the greenhouse during first periods while drawing air from outside to inside the greenhouse and heating drawn in air with heat extracted from the vented air; during second periods between the first periods, drawing in air from outside to inside the greenhouse and heating the air as it is drawn in; and initiating first periods when the relative humidity becomes greater than a predetermined relative humidity.

RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.14/233,156, filed on Mar. 31, 2014, which is a US National Phase of PCTApplication No. PCT/IB2011/053188, filed on Jul. 18, 2011. The contentsand disclosures of each of these prior applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

Embodiments of the invention relate to controlling temperature andhumidity in a greenhouse.

BACKGROUND

Air temperature and relative humidity of an environment in which plantsgrow affect plant growth and health by affecting photosynthesis andtranspiration. Photosynthesis is a process by which plants convertcarbon dioxide and water to organic compounds needed for plant growthand metabolism. Transpiration is a process by which plants draw waterand nutrients required for plant growth and metabolism from soil intotheir roots and transport the water and nutrients to their leaves andother plant organs.

Photosynthesis and transpiration are temperature and relative humiditydependent. Relative humidity, is a ratio equal to an amount of watercontained in the atmosphere per unit volume of air divided by a maximumamount of water a unit volume of the air can contain before the waterbegins to condense out of the air. Water condenses out of air when theair's relative humidity is equal to 100%. Photosynthesis generallyincreases with increase in temperature. Transpiration is affected by arate at which water drawn in from the soil and transported to plantleaves and organs evaporates from surfaces of the leaves and organs andincreases with increase in rate of evaporation. Evaporation of waterfrom plant surfaces also aids a plant in dissipating heat and regulatingplant body temperature. Rate of evaporation and therefore transpiration,and a plants ability to cool itself, generally decreases with increasingrelative humidity.

Plants adapted to different natural environments, for example, desertplants such as cactuses and tropical plants such as orchids, thrive indifferent temperature and relative humidity ranges. If they aresubjected to temperatures and relative humidities outside of the rangesfor which they are adapted, they generally do not do well, and maybecome diseased. Relative humidity in an environment in which a plantgrows that is greater than a maximum for which the plant is adapted canresult in a reduction in rate of evaporation to such an extent thatconcomitant reduction in plant transpiration, and the plant's ability todissipate heat and regulate its body temperature, damages plantmetabolism and health. High relative humidity also tends to result incondensation of water droplets on surfaces of plants when ambienttemperature in the environment decreases during the diurnal cycle. Thecondensed moisture promotes germination of fungal pathogen spores, suchas Botrytis and powdery mildew, on the plant surfaces that can damage orkill the plants.

Because of the sensitivity of plants to temperature and RH, artificialenvironments, such as provided by greenhouses, in which plants arecommercially grown, must generally be monitored and controlled tomaintain air temperature and humidity within desired ranges. For manygreenhouse environments in which leafy plants and vegetables are grown,it is advantageous for temperature to be maintained in a range fromabout 18° C. to about 22° C. and relative humidity in a range from about75% to about 82%.

In the closed environment of a greenhouse, RH tends to increase as aresult of plant transpiration and evaporation of water from the soil andcan be difficult to control. Typically, relative humidity in agreenhouse is controlled using a longstanding conventional procedure, inwhich hot humid air in the greenhouse is periodically vented to theoutside environment and replaced with cooler air drawn into thegreenhouse from the outside. The indrawn cool air is heated to bring itstemperature within a desired range of greenhouse air temperatures.Heating the indrawn cool air also reduces its relative humidity. Thecapacity of air to hold water increases and its RH decreases withincreasing air temperature. Relative humidity of indrawn cool air, evenif it is 100% (i.e. at which relative humidity water begins to condenseout of the air) may be reduced substantially by increasing that air'stemperature. For example relative humidity of outside air at atemperature of 18° C. and 100% relative humidity is decreased to arelative humidity of 50% by heating to a temperature of 25° C.

Whereas the longstanding conventional procedure for controlling relativehumidity by periodically venting hot humid greenhouse air and replacingit with cooler air drawn into the greenhouse from the outside and heatedis generally effective, it exposes greenhouse plants to relatively largefluctuations in air temperature. The procedure also consumes relativelylarge amounts of energy and is therefore expensive.

By way of example, air temperature in a greenhouse using conventionalhumidity control systems may fluctuate from a low temperature equal toabout an outside air temperature, for example, 10° C., to a maximumtemperature of about 22° C. Relative humidity of the inside air maysuffer a range from about 70% to about 100%. During a diurnal cycle forwhich outside relative humidity of outside air fluctuates between about60% to about 70% and temperature of outside air between about 12° C. and16° C. a conventional system may consume more than about 2,000 kWh(kilowatt hours) of energy.

SUMMARY

An embodiment of the invention relates to providing a greenhouseenvironment control (GECO) system for controlling temperature andrelative humidity in a greenhouse by periodically venting warm humid airin the greenhouse and replacing it with air drawn in from the outsidethat is heated by heat extracted from the vented warm humid air. Betweenperiods when warm humid air is vented, the GECO system generates andheats a moderate flow of outside air into the greenhouse. The process isrelatively energy efficient and characterized by relatively moderatefluctuations in greenhouse air temperature that results from exchanginggreenhouse inside air with air from the outside.

In accordance with an embodiment of the invention, the GECO systemcomprises an air circulation and heat exchange system and a controllerthat controls the circulation and heat exchange system selectively tooperate in a “flush” mode or in a “maintenance” mode. The circulationand heat exchange system comprises a first “vent” heat exchanger that iscoupled by a refrigerant fluid and a refrigerant flow system to asecond, “intake” heat exchanger. The vent heat exchanger comprises avent fan system selectively controllable to drive warm moist air frominside the greenhouse to outside the greenhouse or to drive air fromoutside to inside the greenhouse, through a relatively long air flowpath in a large efficient “vent” radiator. The intake heat exchangercomprises an intake fan system controllable to draw relatively cold airfrom outside the greenhouse to inside the greenhouse through arelatively long air flow path in a large and efficient “intake”radiator.

In the flush mode, the GECO controller controls the vent fan system todrive hot humid air from the greenhouse through the vent radiator to theoutside, and the intake fan system to draw air from the outside into thegreenhouse through the intake radiator to replace the vented air. Thevent radiator extracts heat from the vented air to heat the refrigerantfluid and cool the vented air. The refrigerant flow system transportsthe refrigerant heated by heat extracted by the vent radiator from thevented air to the intake radiator. The intake radiator heats air drawninto the greenhouse by the intake fan system and cools the refrigerant.After heat is removed from the refrigerant to heat the intake air, thecooled refrigerant is recycled by the refrigerant flow system to thevent radiator where it is heated again and recycled back to the intakeradiator. Optionally, the vent heat exchanger cools venting air to atemperature substantially equal to an ambient temperature of the outsideair and the intake radiator heats drawn in air to a desired greenhousetemperature.

In the maintenance mode the GECO system operates to maintain temperatureand RH in the greenhouse within desired ranges by generating arelatively slow and steady influx of heated outside air into thegreenhouse. To generate the influx, the GECO controller controls boththe intake and venting fan systems to draw outside air into thegreenhouse and heat the drawn in air to a desired greenhousetemperature. The rate of influx is determined to create an air pressureinside the greenhouse that is slightly greater than atmosphericpressure, and a resultant leakage of air out from the greenhouse equalto the rate of influx. Optionally, air leakage out of a greenhousehaving a floor area of about 1,000 m² (square meter) and height of about3 m is greater than or equal to about 2,500 m³/hr (cubic meters perhour). Optionally, the air leakage is less than about 3,500 m³/hr. In anembodiment of the invention the air leakage may be equal to about 3,000m³/hr (cubic meters per hour). Optionally, the desired greenhousetemperature is equal to about 22° C. To provide heat for heating thedrawn in outside air, the controller couples the refrigerant flow systemto a heat source.

By controlling durations and frequency of switching between flushing andtemperature maintenance modes of operation in accordance with anembodiment of the invention, the GECO system provides substantialsavings in amounts of energy required to control temperature and RH in agreenhouse and reduces amplitude of fluctuations in temperature and RHof air in the greenhouse.

An embodiment of the invention relates to providing a system,hereinafter a water agitator (WAGIT), that operates to clean surfaces ofleaves and plant parts of moisture that may have accumulated on thesurfaces. The system comprises a source of acoustic energy controllableto transmit sound waves which generate vibrations in the leaves andplant parts that agitate and shake water droplets from their surfaces.In an embodiment of the invention, the acoustic source is tunable totransmit acoustic waves at resonant vibration frequencies of plantleaves.

There is therefore provided in accordance with an embodiment of theinvention, apparatus for controlling an environment in a greenhouse, theapparatus comprising: first and second heat exchangers, each comprisinga radiator and a fan system for driving air through the radiator; afirst refrigerant circulation system that circulates a refrigerant fluidbetween and through the radiators; a heater controllable to heat therefrigerant; a controller that controls the apparatus to operateselectively in a maintenance mode or a flush mode, wherein in themaintenance mode the heater heats the refrigerant and the first andsecond fan systems drive air from outside to inside the greenhouse andthrough the radiators to acquire heat from the refrigerant, and in theflush mode the first fan system vents air from inside to outside thegreenhouse through its respective radiator to deposit heat in therefrigerant and the second fan system drives air from outside to insidethe greenhouse and through its respective radiator to acquire the heatdeposited in the refrigerant. Optionally the apparatus comprises a thirdheat exchanger controllable to heat air inside the greenhouse.Optionally, the third heat exchanger comprises a radiator, a secondrefrigerant flow system that streams a refrigerant through the radiator,a heater that heats the refrigerant in the second refrigerant flowsystem and a fan system that drives air inside the greenhouse throughthe radiator to acquire heat from the refrigerant and remain in thegreenhouse.

Optionally the apparatus comprises a fluid flow control valvecontrollable to connect the first and second refrigerant flow systems sothat heated refrigerant from the second refrigerant flow system can flowinto the first refrigerant flow system. Optionally, in the maintenancemode, the controller controls the fluid control valve to connect thefirst and second refrigerant flow systems.

In an embodiment of the invention, in the maintenance mode, thecontroller controls the third heat exchanger to substantially refrainfrom heating air inside the greenhouse.

In an embodiment of the invention, the controller controls the thirdheat exchanger to heat air inside the greenhouse when temperature of theinside air drops below a predetermined minimum air temperature.

In an embodiment of the invention, in the maintenance mode thecontroller controls the fan systems of the first and second heatexchangers to draw air from outside to inside the green house at anaverage flow rate that is substantially proportional to a volume of thegreenhouse. Optionally, the flow rate is greater than about 2,500 m³/hr(cubic meters per hour) per 3,000 m³ of greenhouse volume. Additionallyor alternatively, the flow rate is less than about 3,500 m³/hr per 3,000m³ of greenhouse volume. Optionally, the flow rate is equal to about3,000 m³/hr per 3,000 m³ of greenhouse volume.

In an embodiment of the invention, the controller controls the apparatusto operate in a flush mode if relative humidity in the greenhouse isgreater than a predetermined minimum relative humidity.

In an embodiment of the invention, the controller switches operation ofthe apparatus between flush and maintenance modes at regular intervals.Optionally, duration of a period of operation in the flush mode is thesame for a plurality of consecutive periods of operation in the flushmode. Optionally, the flush mode periods are repeated at a repetitionfrequency greater than about 0.8 per hour. Additionally oralternatively, the repetition frequency is less than about 1.2 per hour.In an embodiment of the invention, the repetition frequency is equal toabout 1 per hour.

In an embodiment of the invention, periods of operation in the flushmode have duration less than or equal to about 10 minutes. In anembodiment of the invention, periods of operation in the flush modeduration greater than or equal to about 5 minutes. In an embodiment ofthe invention, periods of operation in the flush mode have durationequal to about 6 minutes. In an embodiment of the invention, thecontroller initiates periods of operation in the maintenance modesubstantially at times at which periods of operation in the flush modeend.

There is further provided in accordance with an embodiment of theinvention, a method of controlling an environment in a greenhouse, themethod comprising: periodically, during first periods, venting air frominside to outside the greenhouse while drawing air from outside toinside the greenhouse and heating drawn in air with heat extracted fromthe vented air; and during second periods between the first periods,drawing in air from outside to inside the greenhouse and heating the airas it is drawn in.

Optionally the method comprises initiating first periods when therelative humidity becomes greater than a predetermined relativehumidity. Alternatively or additionally the method comprises switchingbetween first and second periods at regular intervals. Optionally themethod comprises determining a same duration for a plurality ofconsecutive first periods.

In an embodiment of the invention the method comprises initiating secondperiods substantially at times when first periods end.

In an embodiment of the invention, an average flow rate at which air isdrawn in from outside to inside the green house during the secondperiods is substantially proportional to the greenhouse volume.Optionally, the flow rate is greater than about 2,500 m³/hr per 3,000 m³of greenhouse volume. Additionally or alternatively, the flow rate isless than about 3,500 m³/hr per 3,000 m³ of greenhouse volume.Optionally, the flow rate is equal to about 3,000 m³/hr per 3,000 m³ ofgreenhouse volume.

In an embodiment of the invention, first periods have duration less thanor equal to about 10 minutes. In an embodiment of the invention, firstperiods have duration greater than or equal to about 5 minutes. In anembodiment of the invention, first periods have duration equal to about6 minutes.

There is further provided in accordance with an embodiment of theinvention, a method of removing water droplets from surfaces of plantsgrowing in a greenhouse, the method comprising: providing an acousticgenerator configured to generate acoustic waves in the greenhouse; andoperating the acoustic generator to transmit sound waves that areincident on, and generate vibrations in, surfaces of the plants thatcause water droplets on the surfaces to roll or be shaken off thesurfaces. Optionally, the sound waves are characterized by a frequencythat is substantially equal to a resonant frequency of vibration of theplant surfaces. Additionally or alternatively, the sound waves arecharacterized by a frequency that is substantially equal to a resonantfrequency of vibration of the water droplets.

In the discussion unless otherwise stated, adjectives such as“substantially” and “about” modifying a condition or relationshipcharacteristic of a feature or features of an embodiment of theinvention, are understood to mean that the condition or characteristicis defined to within tolerances that are acceptable for operation of theembodiment for an application for which it is intended.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF FIGURES

Non-limiting examples of embodiments of the invention are describedbelow with reference to figures attached hereto that are listedfollowing this paragraph. Identical structures, elements or parts thatappear in more than one figure are generally labeled with a same numeralin all the figures in which they appear. Dimensions of components andfeatures shown in the figures are chosen for convenience and clarity ofpresentation and are not necessarily shown to scale.

FIG. 1A schematically shows a conventional environment control systemoperating to maintain temperature and relative humidity in a greenhouse;

FIG. 1B shows a flow chart descriptive of operation of the conventionalenvironment control system shown in FIG. 1A;

FIGS. 1C and 1D show graphs of relative humidity and temperaturerespectively of air in a greenhouse environment controlled by theconventional environment control system shown in FIG. 1A; and

FIG. 2A schematically shows a GECO greenhouse environment control systemoperating to maintain temperature and relative humidity in a greenhouse,in accordance with an embodiment of the invention;

FIG. 2B shows a flow chart descriptive of operation of the GECO systemshown in FIG. 2A, in accordance with an embodiment of the invention;

FIGS. 2C and 2D show graphs of relative humidity and temperaturerespectively of air in a greenhouse environment controlled by the GECOsystem shown in FIG. 2A, in accordance with an embodiment of theinvention; and

FIG. 3 schematically shows operation of a WAGIT moisture removal systemoperating to remove moisture from a leaf in accordance with anembodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description, components and operation of aconventional greenhouse environment control system are described anddiscussed with reference to FIGS. 1A and 1B. FIGS. 1C and 1D show graphsof relative humidity and temperature of air in a greenhouse environmentcontrolled by conventional environment control system such as that shownin FIG. 1A. Components and operation of a GECO environment controlsystem in accordance with an embodiment of the invention are describedand discussed with reference to FIGS. 2A and 2B. FIGS. 2C and 2D showgraphs of relative humidity and temperature of air in a greenhouseenvironment controlled by a GECO system in accordance with an embodimentof the invention such as the GECO system shown in FIG. 1A. Operation ofa WAGIT system for accelerating removal of water from plant surfaces isdiscussed with reference to FIG. 3.

FIG. 1A schematically shows a greenhouse 20 having windows 22 andexhaust fans 24 mounted respectively in opposite walls 26 and 28 of thegreen house. Greenhouse 20 comprises a conventional environment controlsystem 30 for controlling temperature and RH in the greenhouse. Theenvironment control system comprises an “inside” heat exchanger 40 forheating air inside greenhouse 20 to a desired temperature, manifold flowsleeves 60 for distributing the heated air to different regions in thegreenhouse and sensors 31 and 32 for monitoring temperature and RHrespectively of air inside the greenhouse. A controller 33 controls theenvironment control system, windows 22 and exhaust fans 24 of greenhouse20 responsive to measurements of temperature and RH provided by sensors31 and 32.

Heat exchanger 40 comprises a radiator 42 and a refrigerant flow systemcomprising a refrigerant heater 41 and a refrigerant pump (not shown)that streams heated refrigerant, generally water, into and out of theradiator. The refrigerant flow system is connected to radiator 42 byinlet and outlet pipes 43 and 44 respectively. Heat exchanger 40optionally comprises two blowers 46 controllable to drive air in thegreenhouse through radiator 42, where the air is heated to a desiredtemperature by the refrigerant streaming through the radiator. Heatedrefrigerant enters radiator 42 via inlet pipe 43 and after heatinggreenhouse air blown through the radiator by blowers 46, the refrigerantis cooled and leaves the radiator via outlet pipe 44 to return to therefrigerant flow system and heater 41 where it is reheated and returnedto again flow through the radiator. It is noted that in FIG. 1A andfigures that follow, heater 41 is schematically shown located ingreenhouse 20 and close to heat exchanger 40. Heater 41 does not ofcourse have to be located inside greenhouse 20, and in practice theheater is generally located outside the greenhouse, and often far fromthe green house.

Air blown through and heated in radiator 42 flows out of heat exchanger40 and, optionally, into manifold flow sleeves 60 through couplingsleeves 62. The manifold sleeves are typically made of plastic sheetingand/or fabric, and are inflated by the heated air that enters them fromthe heat exchanger. Sleeves 60 are formed having holes (not shown)through which heated air from heat exchanger 40 flowing in the sleevesflows out of the sleeves to mix with air in the greenhouse to maintain adesired greenhouse air temperature and relative humidity. Arrows 64schematically represent air flowing out of sleeves 62. Whereas in FIG.1A heated air exiting heat exchanger 40 is directed into manifoldsleeves 60 for dispersion into the greenhouse volume, in somegreenhouses heated air is dispersed differently. For example, in somegreenhouses heated air from a heat exchanger flows directly from theheat exchanger into the greenhouse volume. By way of another example, insome greenhouses heated water is streamed through a network of pipes onthe greenhouse floor to heat the air inside the greenhouse.

Controller 33 optionally controls environment control system 30 tocontrol temperature and relative humidity in greenhouse 20 byperiodically replacing hot humid air inside the greenhouse with airdrawn in from the outside and heated, in accordance with a conventionalexemplary algorithm schematically represented by a flow diagram 100shown in FIG. 1B. The numeral 100 is used to refer to the flow diagramand to the algorithm which it represents.

Generally, a greenhouse environment control system, such as environmentcontrol system 30, is off during the day in climates for which there issufficient solar energy incident on the greenhouse to maintaingreenhouse air temperature above a desired minimum. In flow diagram 100it is assumed that initially, as shown in a block 102 of the flowdiagram, that controller 33 controls heat exchanger 40 to be off andtherefore environment control system 30 to refrain from heating air ingreenhouse 20.

In a block 104, controller 33 optionally acquires a measurement “T” ofair temperature in greenhouse 20 from temperature sensor 31. In adecision block 106 the controller determines if the measured temperatureT is less than a predetermined desirable minimum temperature “T_(Min)”.Whereas T_(Min) is dependent upon a type of plants grown in greenhouse20, for many plants T_(Min) is advantageously equal to about 20° C. If,in decision block 106, controller 33 determines that T is less thanT_(Min), as generally might occur towards nightfall, the controlleroptionally proceeds to a block 108 and turns on heat exchanger 40 toheat air in greenhouse 20 to a temperature above T_(Min). Turning on theheat exchanger generally involves turning on blowers 46 and therefrigerant flow system to stream hot refrigerant through radiator 42(FIG. 1A). Thereafter, controller 33 optionally proceeds to a block 110.

If instead of finding in decision block 106 that T is less than T_(Min)as assumed in the preceding paragraph the controller 33 finds that T isgreater than or equal to T_(Min) the controller skips block 108 andproceeds to block 110.

In a block 110, whether or not controller 33 skips block 108, thecontroller acquires a measurement “RH” of relative humidity of the airin greenhouse 20 from humidity sensor 32 and in a block 112, thecontroller compares RH to a given desired maximum, “RH_(Max)”. In adecision block 112 the controller also, optionally, determines whetherat a time at which RH is acquired in block 110, an elapsed time sinceair in the greenhouse was last replaced by heated air from the outsideis greater than an optionally predetermined time interval “τ”. If indecision block 112 RH is less than RH_(Max), or the elapsed time is lessthan τ, controller 33 skips a block 114 discussed below, and advances toa block 116.

In block 116 the controller acquires a temperature measurement T, and ina decision block 118 determines whether T>T_(Min). If T is greater thanT_(Min) the controller returns to block 102 and turns off heat exchanger40. On the other hand, if T≦T_(Min), controller 33 returns to block 110,acquires measurement new RH, and in block determines if the new RH isgreater than RH_(Max).

If in decision block 112 controller 33 determines that RH is greaterthan RH_(Max) and the elapsed time is greater than τ, controller 33proceeds to block 114 to replace overly humid air in greenhouse 20 withoutside air to reduce humidity in the greenhouse. To accomplish thereplacement, the controller opens windows 22 and controls fans 24 tovent air from inside greenhouse 20 and draw air in from the outsidethrough open windows 22 to replace the vented air.

In block 116, after replacement of air in greenhouse 20, controller 33acquires a temperature measurement T, and in decision block 118, ifT>T_(Min) the controller returns to block 102 and turns off heatexchanger 40. On the other hand, if T<T_(Min), controller 33 continuesto heat air (block 108) in greenhouse 20 and returns to block 110.

Generally air drawn in from outside greenhouse 20 to replace air insidethe greenhouse is relatively cold, and typically has a temperature thatis substantially less than T_(Min). As a result, immediately afterreplacing air inside greenhouse 20 with outside air, temperature of airin greenhouse 20 is less than T_(Min). For a period after airreplacement therefore, from decision block 118 controller 33 generallyrepeatedly returns to block 110 to cycle through blocks 110-118, heatingair in greenhouse 20 until the controller determines in decision block118 that temperature of air in the greenhouse is greater than thedesired minimum T_(Min).

For many greenhouse environments RH_(Max) is advantageously equal toabout 85%. Time interval τ is determined to prevent cold air fromoutside greenhouse 20 being drawn in to replace greenhouse air sofrequently that a rate at which cold air drawn into greenhouse 20 mustbe heated to maintain a desired greenhouse temperature exceeds acapacity of the heat exchanger to heat the drawn in air.

FIGS. 1C and 1D show graphs 201 and 202 of relative humidity andtemperature respectively of air inside and outside of greenhouse 20having an environment control system 30 operating in accordance with analgorithm similar to algorithm 100. In graphs 201 and 202 solid curves211 and 212 show relative humidity and temperature respectively for airinside greenhouse 20 as a function of time for a period of two days.Time in hours is shown along the graphs' abscissas. Dotted curves 214and 215 show relative humidity and temperature respectively for airoutside greenhouse 20 as a function of time for the same two day period.The curves in graphs 201 and 202 were experimentally determined for agreenhouse, hereinafter also referred to as a 3 m×1,000 m² greenhouse,having height equal to about 3 m and floor space equal to about 1,000m². Heat exchanger 40 when turned on provided 290 kW of energy to heatair streaming at 14,000 m³/hr (cubic meters/hr) through radiator 42. Onthe average, for each diurnal cycle the heat exchanger operated forabout seven hours. In consequence, conventional environment controlsystem 30 consumed about 2,030 kWh (kilowatt hours) of energy duringeach diurnal cycle.

From the graphs it is seen that both relative humidity and temperatureof air in greenhouse 20 cyclically fluctuate with relatively largeamplitudes in cadence with the repeated replacement of hot humidgreenhouse inside air with cold, relatively low humidity outside air.Temperature fluctuates with amplitude of about 7° C. between about 14°C. and about 21° C. and relative humidity fluctuates with an amplitudeof about 20% between about 75% and 95%.

FIG. 2A schematically shows a greenhouse 320 comprising a greenhouseenvironment control system 330, that is a GECO system 330, also referredto as GECO 330, used to control the environment in the greenhouse, inaccordance with an embodiment of the invention.

GECO system 330 optionally comprises components, such as an inside heatexchanger 40 and vent fans 24 comprised in environment control system30, and in addition comprises an air circulation and heat exchangesystem 340, hereinafter also referred to as a climate control system(CCS) 340, in accordance with an embodiment of the invention.

CCS 340 optionally comprises a controller 342 and a vent heat exchanger350 coupled by a refrigerant fluid flow system 360 to an intake heatexchanger 370. Vent heat exchanger 350 comprises a vent radiator 352 andvent fan system 354. The vent fan system is selectively controllable todrive warm moist air from inside the greenhouse to outside thegreenhouse or to drive air from outside to inside the greenhouse,through a relatively long air flow path in a large efficient “vent”radiator 352. Airflow arrows 355 pointing from vent heat exchanger 350towards the outside of greenhouse 320 and airflow arrows 356 pointingfrom the vent heat exchanger towards the inside of the greenhouse,schematically represent the selectable directions in which vent fansystem 354 can drive air. Intake heat exchanger 370 comprises an intakefan system 374 controllable to draw relatively cold air from outside thegreenhouse in a direction indicated by airflow arrows 371 to inside thegreenhouse through a relatively long air flow path in a large andefficient “intake” radiator 372.

Fluid flow control system 360 comprises refrigerant circulation pipes362 that connect intake radiator 372 with vent radiator 352 and arefrigerant pump 364 controllable to pump refrigerant in the circulationpipes between the vent and intake radiators. Circulation pipes 362 areconnected by a fluid flow control valve 366 to inlet pipe 43 throughwhich hot refrigerant from refrigerant heater 41 is introduced intoradiator 42. The circulation pipes are optionally connected by a T joint367 to outlet pipe 44 through which relatively cold refrigerant leavesradiator 42. Controller 342 controls heat exchanger 40, and controlsflow valve 366, pump 364, vent and intake heat exchangers 350 and 370 toselectively operate CCS in a flush mode or a maintenance mode.

In the flush mode, controller 342 controls vent fan system 354 to driveair from inside greenhouse 320 in a direction indicated by airflowarrows 350 to outside of the greenhouse and intake fan system 374 todrive air from outside the greenhouse to inside the greenhouse in adirection indicated by airflow arrows 371. In the flush mode thecontroller closes flow valve 366 and operates refrigerant pump 364 tocirculate refrigerant from vent radiator 352 to intake radiator 372.

Hot humid air driven by vent fan system 354 through vent radiator 352 inthe direction of airflow arrows 355 is cooled in passing through thevent radiator and heats refrigerant fluid in the radiator. Pump 364pumps heated refrigerant from the vent radiator to intake radiator 372where it is cooled in heating air driven by intake fan system 374through the intake radiator. In the flush mode CCS 340 replaces hothumid air vented by vent heat exchanger 350 from inside greenhouse 320with cold air drawn into the greenhouse by intake heat exchanger 370 andheats the indrawn air with heat that the vent heat exchanger extractsfrom the vented air. In an embodiment of the invention, heat extractedfrom the vented air is sufficient to heat indrawn air to a temperaturesubstantially equal to a desired greenhouse air temperature.

In the maintenance mode, controller 342 controls vent fan system 354 todrive air from outside greenhouse 320 to inside the greenhouse in adirection of airflow arrows 356 and intake fan system to drive air fromoutside to inside in a direction of airflow arrows 371. The controlleralso opens flow valve 366 to connect circulation pipes 362 to inlet pipe43 so that refrigerant fluid in the inlet pipe heated by heater 41 thatheats refrigerant fluid for heat exchanger 40 can enter circulationpipes 362. Controller 342 operates pump 364 to circulate the heatedrefrigerant fluid entering the pipes from inlet pipe 43 throughradiators 352 and 372 to heat air drawn in from the outside by vent andintake fan systems 354 and 374. The controller controls a flow rate atwhich the indrawn and heated air enters greenhouse 320 so that airpressure in the greenhouse is slightly greater than atmospheric pressureand heated air from outside flows into the greenhouse at a moderate rateand replaces air inside the greenhouse.

In an embodiment of the invention, controller 342 controls switchingbetween flushing and maintenance modes of CCS 340, and durations of themodes, to maintain a relatively steady response to changes intemperature and relatively humidity of air in greenhouse 320. Cycling ofCCS 340 between flushing and maintenance modes obviates the periodicgreenhouse air replacements that characterize operation of conventionalgreenhouse environment control systems and provides relatively efficientcontrol of greenhouse temperature and relative humidity. FIG. 2B shows aflow diagram 400 of an exemplary algorithm, also referenced by numeral400, that describes operation of GECO 330 in controlling temperature andhumidity in greenhouse 320, in accordance with an embodiment of theinvention.

In flow diagram 400 it is assumed that, as in flow diagram 100 (FIG.1B), initially, GECO 330 is in a quiescent state, in which radiators 42,352 or 372 are not operating to heat air in or being drawn intogreenhouse 320. Accordingly, a block 402 of the flow diagram shows thatgreenhouse heating is off. In a block 404 controller 342 receives ameasurement “T” of temperature in greenhouse 320 from temperature sensor31 and a measurement “RH” of relative humidity of air in the greenhousefrom humidity sensor 32. In a decision block 406, if T is greater than adesired minimum temperature T_(Min) for example, 20° C., controller 342returns to block 402. If however, T is less than or equal to T_(Min), ina block 408 the controller turns inside heat exchanger 40 on, and in ablock 410 turns CCS 340 (FIG. 2A) on in the flush mode. In the flushmode as noted above, heat exchanger 350 is turned on to vent air frominside greenhouse 320 and extract heat from the vented air and heatexchanger 370 is turned on to draw air into the greenhouse from theoutside and heat the drawn in air with the heat extracted from thevented air. In a block 412 controller 342 acquires another measurement Tof temperature and another measurement RH of relative humidity.

In a decision block 414 controller 342 determines whether T is less thanor equal to T_(Min). If T≦T_(Min), the controller leaves inside heatexchanger 40 on and CCS 340 in the flush mode, and returns to block 412,to acquire further measurements of T and RH and in decision block 414 tocompare T to T_(Min). If on the other hand, in decision block 414 thecontroller determines that T>T_(Min), the controller continues to adecision block 416 and determines whether RH<RH_(Max). If RH is greaterthan or equal to RH_(Max), the controller optionally turns off insideheat exchanger 40 in a block 418 and returns to block 412 to again cyclethrough to block 418 leaving inside heat exchanger 40 off, until indecision block 416 controller 342 determines that a measurement RH isless than RH_(Max). Upon determining that RH is less than RH_(Max)controller 342 proceeds to a block 420 and switches CCS 340 to themaintenance mode.

In a block 422 controller 342 acquires measurements of T and RH and in ablock 424 determines whether T≦T_(Min). If T less than or equal toT_(Min), the controller returns to block 408 to turn on inside heatexchanger 40, turn on CCS 340 in the flush mode, and cycle throughblocks in flow diagram 400 to block 424. If in decision block 424T>T_(Min), in a block 426 controller 342 determines whether temperatureT is greater than a maximum desirable temperature T_(Max). If T isgreater than T_(Max) the controller returns to block 402 and shuts downheating of air inside greenhouse 320. Optionally, T_(Max) is atemperature equal to about 22° C. If on the other hand, T is less thanor equal to T_(Max), the controller proceeds to a decision block 428 todetermine whether RH<RH_(Max). If RH is less than RH_(Max), thecontroller leaves CCS 340 in the maintenance mode and returns to block422. If on the other hand RH is greater than or equal to RH_(Max), thecontroller returns to block 410 and switches CCS 340 to operation in theflush mode.

Operation of GECO system 330 in accordance with an algorithm, such asalgorithm 400 reduces magnitude of fluctuations in greenhousetemperature and relative humidity, and results in substantial savings incosts and amounts of energy required to control temperature and relativehumidity in a greenhouse. FIGS. 2C and 2D show graphs 501 and 502 ofrelative humidity and temperature respectively of air inside and outsideof greenhouse 320 controlled by a GECO system similar to GECO system 330operating in accordance with an algorithm similar to algorithm 400.

In graphs 501 and 502 solid curves 511 and 512 respectively showrelative humidity and temperature respectively for air inside greenhouse320 as a function of time for a period of two days. Time in hours isshown along the graphs' abscissas. Dotted curves 514 and 515 showrelative humidity and temperature respectively for air outsidegreenhouse 20 as a function of time for the same two day period.

The curves in graphs 501 and 502, as were the curves in graphs 201 and202 (FIGS. 1C and 1D), were experimentally determined for a 3 m×1,000 m²greenhouse. Vent and intake radiators 352 and 372 had a length in adirection of air flow through the radiators equal to about 100 cm and across section perpendicular to the air flow equal to about 60 cm×60 cm.Each radiator comprised in its 100 cm×60 cm×60 cm volume, an array of 16sets of 16 rows each of ⅝ inch copper pipe. Fan systems 354 and 374 werecapable of streaming 1,500 m³/h (cubic meters of air per hour) throughtheir respective associated radiators. Heat exchangers 350 and 370 werecapable of extracting heat from heated water flowing through theircopper pipes, or introducing heat into cooled water flowing in the pipesat rate of about 10 kW. Heat exchangers 350 and 370 were turned on forabout 7 hours during each diurnal cycle. Whereas, when turned on, heatexchanger 40 in GECO system 330, operated at an energy consumption ofabout 290 kW, during each diurnal cycle it was turned on for about threeand a third hours. An overall average energy consumption of GECO system330 per diurnal cycle was about 1030 kWh.

From graphs 501 and 502 it is seen that neither the relative humidity,curve 511, and temperature of air, curve 512, in greenhouse 320 exhibitthe large cyclical changes exhibited by relative humidity andtemperature controlled by conventional environment control system 30 ingreenhouse 20 (FIG. 1A). Temperature in greenhouse 320 fluctuates withamplitude of about 2° C. between about 20° C. and about 22° C., andrelative humidity in the greenhouse fluctuates with an amplitude ofabout 8% between about 80% and about 87%. Not only does GECO system 330provide substantially improved control of temperature and relativehumidity in a greenhouse but it does it with substantially reducedenergy consumption compared to a conventional greenhouse environmentcontrol system.

For example, as noted above, for external conditions of temperature andrelative humidity of outside air indicated by curve 215 in graph 202 andcurve 214 in graph 201 respectively, conventional greenhouse environmentcontrol system 30 may consume about 2,030 kWh of energy per diurnalcycle to control air in greenhouse 20 with proficiency represented bycurves 212 and 211 in the graphs. A GECO system in accordance with anembodiment of the invention similar to GECO system 330 on the otherhand, for conditions of relative humidity and temperature of outside airindicated by curve 514 in graph 501 and curve 515 in graph 502respectively, may control humidity and temperature for greenhouse 320with substantially improved proficiency exhibited by curves 511 and 512in the graphs at an energy cost of 1,030 kWh per diurnal cycle. Whereasthe conditions of temperature and relatively humidity of outside airunder which GECO system 330 operates to control temperature and relativehumidity of air in greenhouse 330 are substantially more demanding thanthe conditions of temperature and relative humidity of outside air underwhich conventional environment control system 30 operates, the GECOsystem operates at an average power consumption that is about half thatat which the conventional system operates.

It is noted that the energy consumption and flow rates referred to abovefor GECO system 330 that controls an environment for a 3 m×1,000 m²greenhouse and provides performance substantially as shown in graphs 501and 502, scale substantially linearly with greenhouse size. For example,a GECO system in accordance with an embodiment of the used to controlthe environment in a 3 m×2,000 m² greenhouse may be configured toconsume twice the energy and provide twice the flow rates provided by aGECO system that controls the environment in a 3 m×1,000 m² greenhouse.

In some embodiments of the invention, controller 342 controls GECO 330to switch between flush and maintenance modes at optionallypredetermined regular intervals. For example, a GECO system similar toGECO 330 in accordance with an embodiment of the invention may operatein flush and maintenance modes for about six and about fifty fourminutes respectively every hour can maintain a greenhouse temperaturebetween about 20° C. and about 22° C., and relative humidity betweenabout 80% and about 87%, for outside air and relative humidites forwhich graphs 501 and 502 were obtained.

To provide added protection for plants against disease encouraged orpromoted by water condensation on plant leaves and body parts, agreenhouse may comprise a WAGIT in accordance with an embodiment of theinvention that operates to sonically clean surfaces of leaves and plantparts of moisture that may have accumulated on the surfaces.

FIG. 3 schematically shows a WAGIT 600 operating to remove waterdroplets 650 condensed on a plant leaf 652, in accordance with anembodiment of the invention. WAGIT 600 optionally comprises an acoustictransducer 602, such as a piezoelectric crystal, driven by a powersource 604 to generate acoustic waves, schematically represented bydashed arcs 610 that propagate to leaf 652. When sonic waves 610 areincident on leaf 652 they generate large amplitude vibrations,represented by dashed silhouettes 654, in the leaf that shake waterdroplets 650 off the leaf. The removal of the water droplets isschematically indicated by arrows 656.

In an embodiment of the invention, power source 604 drives transducer602 to generate waves 610 at a frequency substantially coincident with aresonant frequency of leaf 652. As a result, acoustic waves 610 generaterelatively large vibrations in leaf 652 that are relatively efficient inshaking droplets 650 off the leaf. Optionally, power source 604 drivesacoustic transducer 602 to generate acoustic waves at a resonantfrequency of water droplets 650, which generate relatively largevibrations in the bodies of the droplets. The vibrations cause thedroplet to “roll” off leaf 652.

In the description and claims of the present application, each of theverbs, “comprise” “include” and “have”, and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of components, elements or parts of the subject orsubjects of the verb.

Descriptions of embodiments of the invention in the present applicationare provided by way of example and are not intended to limit the scopeof the invention. The described embodiments comprise different features,not all of which are required in all embodiments of the invention. Someembodiments utilize only some of the features or possible combinationsof the features. Variations of embodiments of the invention that aredescribed, and embodiments of the invention comprising differentcombinations of features noted in the described embodiments, will occurto persons of the art. The scope of the invention is limited only by theclaims.

1. A method of controlling an environment in a greenhouse, the method comprising: periodically venting air from inside to outside the greenhouse during first periods while drawing air from outside to inside the greenhouse and heating drawn in air with heat extracted from the vented air; during second periods between the first periods, drawing in air from outside to inside the greenhouse and heating the air as it is drawn in; and initiating first periods when the relative humidity becomes greater than a predetermined relative humidity.
 2. A method according to claim 1 and comprising switching between first and second periods at regular intervals.
 3. A method according to claim 1 and comprising determining a same duration for a plurality of consecutive first periods.
 4. A method according to claim 1 and comprising initiating second periods substantially at times when first periods end.
 5. A method according to claim 1 wherein an average flow rate at which air is drawn in from outside to inside the greenhouse during the second periods is substantially proportional to the greenhouse volume.
 6. A method according to claim 5 wherein the flow rate is greater than about 2,500 m³/hr per 3,000 m³ of greenhouse volume.
 7. A method according to claim 5 wherein the flow rate is less than about 3,500 m³/hr per 3,000 m³ of greenhouse volume.
 8. A method according to claim 7 wherein the flow rate is equal to about 3,000 m³/hr per 3,000 m³ of greenhouse volume.
 9. A method according to claim 1 wherein first periods have duration less than or equal to about 10 minutes.
 10. A method according to claim 1 wherein first periods have duration greater than or equal to about 5 minutes.
 11. A method according to claim 1 wherein first periods have duration equal to about 6 minutes. 